1. Technical Field
The present disclosure relates to a nonaqueous electrolyte secondary battery.
2. Related Art
In recent years, vehicles utilizing electric energy, such as electric vehicles and hybrid vehicles, have been put into practical use. Along with the development for the higher performance of such vehicles, the development for secondary batteries as the driving power source has been advanced. In particular, a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery has been expected for its characteristics of high output, high capacity (high energy density), and long life.
The nonaqueous electrolyte secondary battery has been required to have small weight and thickness. More and more nonaqueous electrolyte secondary batteries have come to have a package formed of a laminate film instead of a metal can. The laminate film can have small weight and thickness and the processing of the laminate film is easy.
Various examinations have been conducted for improving the performance of the nonaqueous electrolyte secondary batteries. For example, WO 2006/118279 A has disclosed the positive electrode material for a lithium ion battery, which includes secondary particles including primary particles of lithium nickel composite oxide with a different length horizontally and vertically (an aspect ratio of not 1). Here, the vertical direction (longitudinal direction) of at least some primary particles is toward the center of the secondary particle. According to WO 2006/118279 A, the positive electrode material allows fewer cracks of the secondary particles in the discharging cycle at high temperature and with high output.
JP-A-2013-232318 has disclosed the lithium metal composite oxide with a layer structure. The D50 of this composite oxide is more than 4 μm and less than 20 μm, and the area ratio of the primary particle to the secondary particle (primary particle area/secondary particle area) of this composite oxide is in the range of 0.004 to 0.035. The minimum value of the powder crushing strength is more than 70 Ma. According to this patent literature, the lithium secondary battery including this composite oxide as the positive electrode material has the excellent life characteristic, initial charging and discharging characteristic, and slurry characteristic.
JP-A-2006-253119 has disclosed the lithium nickel manganese cobalt composite oxide powder with a layered crystal structure and a particular composition. Of the crystal structure in this patent literature, the lattice constants “a” and “c” satisfy 2.855 Å≤a≤2.870 Å and 14.235 Å≤c≤14.265 Å. According to this patent literature, using this powder as the positive electrode material for the lithium secondary battery leads to the lower cost, the higher withstanding voltage, the higher safety, and the higher battery performance.